timetoa.h revision 1.1
1/* $NetBSD: timetoa.h,v 1.1 2013/12/27 23:30:46 christos Exp $ */ 2 3/* 4 * timetoa.h -- time_t related string formatting 5 * 6 * Written by Juergen Perlinger (perlinger@ntp.org) for the NTP project. 7 * The contents of 'html/copyright.html' apply. 8 * 9 * Printing a 'time_t' has some portability pitfalls, due to it's opaque 10 * base type. The only requirement imposed by the standard is that it 11 * must be a numeric type. For all practical purposes it's a signed int, 12 * and 32 bits are common. 13 * 14 * Since the UN*X time epoch will cause a signed integer overflow for 15 * 32-bit signed int values in the year 2038, implementations slowly 16 * move to 64bit base types for time_t, even in 32-bit environments. In 17 * such an environment sizeof(time_t) could be bigger than sizeof(long) 18 * and the commonly used idiom of casting to long leads to truncation. 19 * 20 * As the printf() family has no standardised type specifier for time_t, 21 * guessing the right output format specifier is a bit troublesome and 22 * best done with the help of the preprocessor and "config.h". 23 */ 24#ifndef TIMETOA_H 25#define TIMETOA_H 26 27#include "ntp_fp.h" 28#include "ntp_stdlib.h" 29#include "ntp_unixtime.h" 30 31/* 32 * Given the size of time_t, guess what can be used as an unsigned value 33 * to hold a time_t and the printf() format specifcation. 34 * 35 * These should be used with the string constant concatenation feature 36 * of the compiler like this: 37 * 38 * printf("a time stamp: %" TIME_FORMAT " and more\n", a_time_t_value); 39 * 40 * It's not exactly nice, but there's not much leeway once we want to 41 * use the printf() family on time_t values. 42 */ 43 44#if SIZEOF_TIME_T <= SIZEOF_INT 45 46typedef unsigned int u_time; 47#define TIME_FORMAT "d" 48#define UTIME_FORMAT "u" 49 50#elif SIZEOF_TIME_T <= SIZEOF_LONG 51 52typedef unsigned long u_time; 53#define TIME_FORMAT "ld" 54#define UTIME_FORMAT "lu" 55 56#elif defined(SIZEOF_LONG_LONG) && SIZEOF_TIME_T <= SIZEOF_LONG_LONG 57 58typedef unsigned long long u_time; 59#define TIME_FORMAT "lld" 60#define UTIME_FORMAT "llu" 61 62#else 63#include "GRONK: what size has a time_t here?" 64#endif 65 66/* 67 * general fractional time stamp formatting. 68 * 69 * secs - integral seconds of time stamp 70 * frac - fractional units 71 * prec - log10 of units per second (3=milliseconds, 6=microseconds,..) 72 * or in other words: the count of decimal digits required. 73 * If prec is < 0, abs(prec) is taken for the precision and secs 74 * is treated as an unsigned value. 75 * 76 * The function will eventually normalise the fraction and adjust the 77 * seconds accordingly. 78 * 79 * This function uses the string buffer library for the return value, 80 * so do not keep the resulting pointers around. 81 */ 82extern const char * 83format_time_fraction(time_t secs, long frac, int prec); 84 85#endif /* !defined(TIMETOA_H) */ 86